Do exactly what bdebde said - short screws, up from the bottom into the spacer and then down through the tray into the spacer.
Take a look at how I mounted the tray from Mike on my XB8 and it will make a little more sense:
http://www.rc-monster.com/forum/atta...9&d=1201098916
You will have to cut about a 1/2" wide piece lengthwise from the plastic spacer piece Mike provides with the tray.